LEED has been widely used to analyze surface structure (crystalline) of solid material by the electron diffraction, i.e., Bragg's diffraction of de Broglie wave of low energy electron. LEED is very sensitive to the atomic arrangement near surface; it provides information of dislocations, impurities and contaminations of solid material. LEED is inevitable device in surface science. See Non Patent Literature No. 1.
However, as shown in Non Patent Literature No. 1, conventional LEED apparatus uses electron energy filters made by spherical shaped metal grids in its detection components, usually 5 cm to 10 cm in diameter. Therefore, the size of the LEED apparatus is large, and the it does not fit to typical equipment ports of commercial SEMs (Scanning Electron Microscopes).
In more detail, in the conventional LEED, thermionic electron gun is used to generate a probe electron beam (typically, 0.1 mm diameter, 1 micro-ampere or less, a few 100 Volts) impinging on a sample surface from the normal direction. The inelastic back-scattered electrons are rejected through energy filtering grids made by spherical shaped metal screens (usually 5 cm to 10 cm in diameter). The elastic back-scattered electrons (diffraction) are detected by phosphor screen and a CCD camera. Because it uses fairly large grids, the conventional LEED does not fit within SEM chambers. Also, because the grids are spherical shape, it is not easy to make finer meshes. When the LEED unit is large, it may interfere with other detectors, such as, STEM detector or XRD detector.
Furthermore, even through Bragg's diffraction is caused by atomic arrangement around sample surface, the conventional LEED does not work for imaging the atomic structure; it just shows averaged Bragg's diffraction from crystalline structure. Reason is that the spot size of the probe electron beam in typical LEED apparatus is around 100 micrometers, which is too large, and finest interference fringes associated between two points at both edges on the spot will exceeds the finest pitch of CCD or CMOS detector, and will be hidden in the diffraction image. As a result, it is not possible to recover the real image using holography or iterative phase retrieval process on the diffraction image.
To obtain image of the atomic structure, we need to make the electron beam spot size on the sample as small as 10 nm to 100 nm (for example, using 2000 pixels CCD, at 1 Angstrom De Broglie wavelength of electron for 150 eV, the spot size should be 100 nm or smaller). One way to achieve this is to use the electron beam of SEM for LEED analysis. The SEM generally uses high quality electron beams suitable for this purpose. However, the SEM electron gun and its column are fairly large; they do not fit within a hole on the grid and the detector of the conventional configuration of LEED.